Recently, an energy management system provided with a power generating apparatus, such as a solar cell and a wind power generating apparatus, has been known.
By the way, although greatly influenced by a power condition of each country, in Japan, for example, the total power rate of a high-voltage power user is defined by a basic rate and a metered power rate. The basic rate is defined based on a peak amount of power in a prescribed period (for example, 30 minutes) in the past. On the other hand, the metered power rate is defined based on the usage amount of power in a calculation target period. A method for determining the power rate in Japan is described in, for example, Patent Literature 1.